The clustering of galaxies as a function of their photometrically estimated atomic gas content

We introduce a new photometric estimator of the H i mass fraction () in local galaxies, which is a linear combination of four parameters: stellar mass, stellar surface mass density, NUV-r colour and g-i colour gradient. It is calibrated using samples of nearby galaxies (0.025 < z < 0.05) with H i line detections from the GALEX Arecibo SDSS Survey (GASS) and Arecibo Legacy Fast ALFA (ALFALFA) surveys, and it is demonstrated to provide unbiased estimates even for H i-rich galaxies. We apply this estimator to a sample of similar to 24 000 galaxies from the Sloan Digital Sky Survey (SDSS)/Data Release 7 (DR7) in the same redshift range. We then bin these galaxies by stellar mass and H i mass fraction and compute projected two-point cross-correlation functions with respect to a reference galaxy sample. Results are compared with predictions from current semi-analytic models of galaxy formation. The agreement is good for galaxies with stellar masses larger than 1010 M?, but not for lower mass systems. We then extend the analysis by studying the bias in the clustering of H i-poor or H i-rich galaxies with respect to galaxies with normal H i content on scales between 100 kpc and similar to 5 Mpc. For the H i-deficient population, the strongest bias effects arise when the H i deficiency is defined in comparison to galaxies of the same stellar mass and size. This is not reproduced by the semi-analytic models, where the quenching of star formation in satellites occurs by starvation and does not depend on their internal structure. H i-rich galaxies with masses greater than 1010 M? are found to be antibiased compared to galaxies with normal H i content. Interestingly, no such effect is found for lower mass galaxies.